Alcohol abuse during pregnancy can profoundly affect the developing fetus, resulting in fetal alcohol syndrome (FAS). Alcohol particularly damages the developing brain, leading to microencephaly, mental retardation, and hyperactivity. One of the leading causes of mental retardation, FAS is a major public health problem. In the developing brain, neuronal death is one of alcohol's most prominent pathologic effects, and this loss of neurons underlies many of the behavioral deficits associated with the syndrome. Neurons are particularly sensitive to alcohol-induced death during the brain growth spurt, a period of rapid brain growth, during which many neurons morphologically mature by extending neurites and forming synaptic connections. Why developing neurons are particularly vulnerable to alcohol during the brain growth spurt is unknown, but may be due to an interaction between alcohol and patterns of gene expression regulating neuronal morphological development. MicroRNAs are small, non-coding RNAs that regulate the development of the central nervous system by controlling the expression of many genes. Two microRNAs of particular importance to brain development are microRNA-132 (miR-132) and miR-124, both of which are enriched in brain and regulate neuronal morphogenesis and neurite outgrowth. The central hypothesis of this proposal is that alcohol disrupts neuronal maturation and renders neurons vulnerable to alcohol toxicity by interfering with miR-132 and miR-124 expression. Thus, the experiments of this proposal will focus on the interaction between alcohol and these microRNAs during brain development. In this proposal, we will determine whether miR-132 and miR-124 expression are developmentally regulated, whether their expression levels are related to periods of alcohol vulnerability, and whether alcohol affects their expression. We will also determine whether experimental manipulations of miR-132 and miR-124 alter neuronal morphology and vulnerability to alcohol. We will determine whether ectopic expression of these microRNAs promotes neurite outgrowth and protects developing neurons against alcohol toxicity. Conversely, we will determine whether silencing of miR-132 and miR-124 impairs neurite outgrowth and increases the vulnerability of developing neurons to alcohol-induced cell death. Thus, these studies will examine the effect of alcohol on two related and important microRNAs and determine their role in maturation-dependent alcohol resistance, a phenomenon of fundamental importance in FAS. PUBLIC HEALTH RELEVANCE: Alcohol abuse during pregnancy can profoundly affect the developing fetus, resulting in fetal alcohol syndrome (FAS). Alcohol damages the developing brain, leading to microencephaly, mental retardation, and hyperactivity. In this proposal we will examine the effect of alcohol on microRNAs, master switches that control the expression of several genes involved in the morphological maturation of neurons.